1. Field of the Invention
The present invention relates to a method for treating a surface using a plasma generated by radio frequency wave source, particularly a microwave or UHF source of energy. In particular, the present invention relates to a method which utilizes a disk shaped plasma allowing etching, texturing, vapor deposition and oxidation of the surface. The present invention also relates to an apparatus for treating the surface of an article, such as an integrated circuit.
In U.S. application Ser. No. 468,897 filed Feb. 23, 1983 and now U.S. Pat. No. 4,507,588, including one of the present inventors, a microwave ion source apparatus is described which is useful for large surface area treatment. This apparatus produces a microwave plasma over the surface being processed. The plasma has a disk shape and hence the name microwave plasma disk reactor. It can be operated continuously from high pressures (over one atmosphere) to low (&lt;10.sup.-3 Torr) pressures in any gas, and is particularly adaptable to many different conditions. This allows the optimization of a given process. In particular input power, gas flow, pressure, and the like can be accurately controlled through large variations, with a sustained plasma. The present invention is an outgrowth of this earlier application.
2. Prior Art
The high density requirement of VLSI (Very Large Scale Integration) technology has provided a driving force for the application of plasma processing to integrated circuit (IC) fabrication. Current and potential uses of plasma assisted semiconductor wafer processing include oxidation, film deposition, and dry etching procedures (Sze, S. M., VLSI Technology, McGraw Hill, New York (1983)). All of these offer advantages to VLSI processing because of one or more of several factors, including anisotropic properties, low temperature which leads to small wafer thermal stress, or improved material quality. Heretofore most IC plasma processing has been carried out with dc or rf generated plasmas (less than or equal to 60 megahertz). However, microwave induced plasmas possess several advantages and several researchers have suggested the investigation of the effect of higher frequencies on plasma processing.
Until recently, with the exception of early work on plasma growth of native oxides in silicon, few experiments have investigated microwave plasma IC processing. Primarily, this is because microwave discharges usually have small volumes and, particularly, small surface areas. On the other hand, microwave discharges have several positive attributes for semiconductor processing. For example, microwave generated plasmas allow higher plasma densities at lower pressures when compared to rf or dc plasmas. A substantially greater degree of anisotropic etching, and therefore high circuit density, should therefore be possible by processing with microwave plasmas. Some Japanese experimental work with microwave discharges appears to confirm this expectation (Suzuki, K. S., S. Okudaira, N. Sadudo and I. Kanomata, "Microwave Plasma Etching," 16, 1979-1984 (1977); Suzuki, K., S. Nishimatsu, K. Ninomiya and S. Okudaira, "Microwave Plasma Etching," Proc. Int'l Ion Engineering Congress ISIAT '83 & IPAT '83, 1645-1656 (1983)) and, in fact, Hitachi has recently introduced a microwave plasma etching system for commercial use (Electronics, p. 63, Nov. 20, 1980). Also microwave plasmas, as is the case for rf but not dc, may be electrodeless which reduces a source of contamination, reduces maintenance and increases lifetime. Microwave systems are of comparatively low cost, are simple to operate, and are usually more efficient than dc or rf plasmas. By moving into the higher frequency range, more excited atomic states and more free radicals are present in the plasma.